1. Field of the Invention
The present invention relates to a pin-type light receiving device used in optical fiber communication or the like, and an optoelectronic integrated circuit in which the pin-type light receiving device and an electronic circuit device are monolithically integrated.
2. Related Background Art
In optical fiber communication or the like, a pin-PD (Photo Diode) is generally used as a light receiving device, especially a light receiving device monolithically integrated together with an electronic circuit device such as an FET (Field Effect Transistor) in a optoelectronic integrated circuit. This pin-PD is mainly formed into a mesa shape from a viewpoint of easy integration or isolation between devices.
In a conventional pin-PD, for example, an n-type semiconductor layer, an i-type semiconductor layer, and a p-type semiconductor layer are sequentially formed on a semiconductor substrate consisting of InP having semi-isulation properties, each semiconductor layer is formed into a mesa shape, and the surface thereof is protected by an insulating layer.
Prior arts about such a mesa type pin-PD are described in detail in, e.g., "Inst. Phys. Conf., ser. no. 96, chap. 8, Int. Symp. GaAs and Related Compounds, pp. 571-574, 1988", "IEEE Photon. Technol. Lett., vol. 2, no. 7, pp. 505-506, 1990", and "Electron. Lett., vol. 26, no. 5, pp. 305-307, 1990".
In the above conventional mesa type pin-PD, upon application of a reverse bias voltage, a depletion layer extending from the p-type semiconductor layer is exposed to the surface of the mesa mainly constituted by the i-type semiconductor layer. More specifically, the depletion layer reaches the interface between the side surface of the i-type semiconductor layer and the insulating layer for protecting the surface of the i-type semiconductor layer. For this reason, in accordance with the interface state, a dark current is generated to flow along the surface of the mesa from the p-type semiconductor layer to the i-type semiconductor layer. Therefore, a large amount of dark current is generated.
In addition, in such an optoelectronic integrated circuit in which a pin-PD and an electronic circuit device are integrated, when the dark current is generated, noise is increased to degrade the receiving sensitivity.